Tim's Time
& Sync Blog

PTP Time Error for T-BCs

The accuracy of Telecom Boundary Clocks (T-BCs) is essential to the successful roll-out of LTE-A and TDD-LTE. To meet the new G.8273.2 compliance limits

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2020 vision

The ITU’s Study Group 15 met in Geneva again this month. Study Group 15 is the group responsible for the optical transport and access networks, including synchronisation.

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Measuring Time Error Transfer of G.8273.2 T-BCs

The companion application note, "Testing a T-BC to ITU-T G.8273.2" (previous blog) describes the methods of testing a telecom boundary clock (T-BC) to meet G.8273.2.

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Testing a T-BC to ITU-T G.8273.2

The accuracy of Telecom Boundary Clocks (T-BCs) is still essential to the successful roll-out of LTE-A and TDD-LTE. With that in mind, we recently revised our application notes on Boundary Clocks.

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TSN/A 2017 show report

The interest in Time Sensitive Networks (TSN) - and its evolution - is clearly of great interest in a number of industry sectors as was demonstrated both in the papers presented at this year’s TSN/A conference in Stuttgart, as well as the diversity in background of delegates.

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ISPCS 2017 show report

Calnex was at the 2017 ISPCS Plugfest & Symposium this year. The event started with a Plugfest where multiple vendors plugged and tested their Precision Timing Protocol (PTP or 1588) equipment. This is a valuable open session where vendors and researchers from different communities can perform real-world connections and tests, which contribute to their development and research processes.

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Partial Support for Partial Timing Support

For a long time now, operators have been asking about how to use PTP to transfer time across their existing networks. Vendors say it’s possible, but the standards are not there. At least, until now. The ITU-T have just taken a big step forward with the agreement of G.8271.2 at their June meeting. What this standard does is define the requirements on the network for PTP to be able to work accurately over existing networks.

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Fronthaul - what's going on?

Following on from the ITU meeting I recently attended, a bit more detail on the Fronthaul topic. In 4G, the “fronthaul” concept was born, separating the baseband unit from the radio unit, and connecting them using dedicated fibre. A protocol was invented, CPRI (Common Public Radio Interface) to carry what was basically the radio signal over the fibre.The radio unit simply had to modulate that signal onto the carrier, so it could be very simple and cheap.

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STAC 2017

STAC (Securities Technology Analysis Center) arrived in London after stops in Chicago and New York and as always with these events, there was as a local focus. The impending MiFID 2 directive, in particular the trade timestamping requirements inevitably played a prominent part in proceedings. In fact timing, sync and latency papers dominated the first half of the event.

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Which BMCA algorithm is in use?

The Best Master Clock Algorithm (BMCA) is run by all PTP ports in a system, and is a distributed algorithm. Initially all ports send out Announce messages advertising their capabilities, and from that each port and each clock determines which source to synchronise to. For a master-capable port, that may include itself, in which case it becomes a grandmaster.

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Stop The Clocks!

Stop the clocks! WSTS is now over for another year, so here are a few highlights from this year’s show.

One of the keynote speeches came from Han Li of China Mobile. Han is responsible for planning China Mobile’s network strategy for 5G, including how to handle synchronisation.

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Geek Glastonbury or B2B Burning Man?

What value could an SME get from attending a suited & booted funfair with almost 100,000 others?

Mobile World Congress, a forum of just about anything with a connection to the mobile network has seen a surge of interest, relevance and of participation in recent years.

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RMS or Peak-to-Peak Jitter?

Excessive jitter impacts the ability of clock recovery circuits to recover the clock properly which can lead to mistiming inside transmission equipment when data is regenerated. When timing errors becomes large, bit errors are introduced leading to excessive packet loss. Jitter is generally expressed in terms of Unit Intervals where a Unit Interval (UI) equals one bit time of a digital NRZ binary signal.

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Events in the synchronization world from 2016

For the first blog of the new year, I’m going to look back at some of the significant events in the synchronization world from 2016. The year got off to an interesting start with a reminder that we can’t always trust GPS. Back in January, the GPS system started putting out the wrong time. This wasn’t caused by jamming or spoofing, but was a configuration error caused by trying to de-commission an old satellite.

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First 5G sync recommendation

The ITU approved two new recommendations on synchronisation this weekend. G.8272.1 is the first “enhanced” clock specification aimed at meeting the requirements for 5G mobile infrastructure. The document specifies the enhanced PRTC (Primary Reference Time Clock), basically a very high accuracy GNSS timing receiver, capable of delivering time to within 30ns of UTC.

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Timing not Telecoms

I just got back from Prague after the ITSF 2016 conference. If you weren’t there, you missed another great event in a beautiful city. You can always book for next year, when the conference will be in Warsaw, Poland, of if you can’t wait that long, there is always the WSTS conference in San Jose, California in the first week of April.

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Sync University

I recently had a question on “Ask Tim” about a great sync knowledge source - a website called 'Sync University'. The questioner found it extremely useful with lots of great content but was now unable to find it anywhere.

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Quality or Traceability?

I recently had a question on “Ask Tim” about how to distinguish between a packet-based frequency signal, delivered using the PTP profile in G.8265.1, and a Synchronous Ethernet signal delivered using the Ethernet physical layer.

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1 million connections per square km with 5G

Virtual Birth? About 15 years ago, I remember reading a book on the future of telecoms. At the time, the 3G mobile system was just in development, and the ultimate 3G speed was projected to be 384 kbit/s (compared to the 56kbit/s I was getting to my house).

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What is PTP?

What is PTP? PTP stands for “Precision Timing Protocol”, and is described in IEEE Standard 1588. It is a protocol for distributing time across a packet network. It works by sending a message from a master clock to a slave clock, telling the slave clock what time it is at the master.

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High Speed Jitter

Jitter has been around for as long as the telecommunications industry has been trying to shift bits and bytes from A to B. Jitter is not cool, it’s unloved and nobody wants it and just like the bore at an office party it won’t go away. Now, just to be clear, we are talking about physical layer jitter here

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The emergence of 5G

I am just finished talking with the CEO of Calnex, Tommy Cook who had just completed a series of customer visits in Japan and China. The chat amongst the operators about 5G being just over the horizon is starting. Tommy went on to say ...

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Timestamping requirements

Quote of the day: “Clock sync is a pain, princess. Anyone who tells you differently is selling you something.” Neil Horlock, at the MiFID II Workshop on 26th May 2016 . This was a workshop on how to meet the timestamping requirements set out in MiFID II, the latest European legislation on financial markets.

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Time Sensitive Networking

There’s a buzz around the topic of Time Sensitive Networking at present. It is being linked with the “Industrial Internet of Things” (IIoT), although it is not exclusively about industrial networks. The concept began with audio and video distribution as the “Audio/Video Bridging” group of IEEE, and is now being extended to cover industrial

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What is a Clock?

Following on from my post “What is Time?”, a clock is simply a device that counts regular events from a common starting point. That applies to all clocks and calendars, with the possible exception of a sundial! The regular events might be days, months and years, or they might be pendulum swings, quartz vibrations, or atomic transitions.

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Partial Progress?

ITU's Study Group 15, the body associated with transmission and networks, met in Geneva recently. One interesting statistic I heard during that meeting was that Question 13, the synchronization sub-group, receives as many contributions as some entire study groups. Synchronization is far and away the biggest “Question” within ITU.

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Confusion Rules!

The only thing that's standard is confusion! Why does ITU say this, and IEEE say that? What on earth is MEF doing? I see Small Cell Forum are in on the act? Why can’t 3GPP sort out what they want? I saw a cartoon recently that explained neatly why we have so many different standards for the same thing ...

Show cartoon...

What is Time Error?

Your watch says you have a minute to go. You walk into the meeting room all set, and a sea of angry faces look up at you, saying “Where have you been? You’re late!” What went wrong?

The answer is your watch – it was 5 minutes out. This is called time error. It is the difference between the time reported by a clock (or watch), and the reference clock (for example, the clock on the meeting room wall).

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Prolific Profiles

IEEE1588 (2008) is a huge standard, 269 pages long. It defines the Precision Time Profile (PTP), a protocol for distributing time aver a packet network. Thing is, types of packet networks are 10 a penny these days.

There are industrial networks, power networks, telecom networks, audio networks, video networks, in-car networks just to name a few. All have subtly different requirements and therefore IEEE1588 contains loads of different options and features that simply aren’t appropriate for every network.

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Basestations need Sync

One of the biggest drivers behind the renewed interest in time and synchronization is the mobile industry. The latest generation of mobile technology requires that the basestations are not only synchronized in frequency, but in time too. This is because many of the techniques used for increasing capacity in the mobile

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Unravelling Standards

Traditionally, timing and synchronization has been slow moving, pedestrian, and not very exciting. Not much to write about! However, that has changed in recent years. I attended my first ITU-T meeting on synchronization back in 2004. We had seven attendees and eleven contributions to consider. Now, we often get 35 – 40 attendees

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What is SyncE?

When the telephone networks started to go digital in the 1960s, the voice sampling frequency was carried in the physical layer of the multiplexed digital voice signal.

This frequency was transported across the network so that all voice switches could operate at the same frequency, as any mismatch would cause clicks and pops in the voice channel.

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Interpreting ITU

The ITU has produced over a dozen standards to do with time and synchronization over the last ten years. Why so many? Partly it’s a matter of evolution, and partly it’s a matter of purpose.

The first standard released back in 2006 was G.8261, and it covered “general aspects” of frequency distribution in packet networks. Time wasn’t a topic back then. G.8261 evolved into a set of standards for frequency distribution:

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Tick Talk

Since this blog is all about time, it might be useful to try and explain what time is. So this is me trying to do what countless philosophers, theologians and physicists have been attempting to do for centuries.

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LTE-A & VoLTE rollout

GSA confirms 393 LTE networks launched, year end forecast raised, LTE-Advanced and VoLTE deployments booming April 9, 2015: 393 operators have commercially launched LTE in 138 countries. This is according to data released today by GSA (Global Mobile Suppliers Association) in the latest update of the Evolution to LTE report.

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LTE picks up speed

Long-term evolution, better known as LTE, had a blockbuster year in 2014. More than 110 commercial LTE networks went live, and global LTE subscriptions topped 250 million in the first quarter of 2014.

LTE is now commercially available in more than 107 countries, and mobile network operators added 109 LTE networks between June 2013 and June 2014. As you can see below in Figure 1, LTE is everywhere.

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